U.S. Pat. No. 4,895,610 to Egan relates to a pneumatic tire which contains a built-in sealant layer prepared by building a layer of butyl rubber-based composition, which contains a polyisobutylene polymer, following which under the conditions of elevated temperature and pressure used to cure the tire, a major portion of the butyl rubber is presented as being both crosslinked and depolymerized to form a tacky material which has puncture sealant properties.
U.S. Pat. Nos. 4,228,839, 4,171,237 and 4,140,167 also relate to a sealant layer in a tire formed by depolymerizing and crosslinking a butyl rubber based rubber composition, particularly by irradiation treatment
Patents relating to tire constructions, sealant compositions and methods wherein a sealant material is encased or encapsulated in between calendered layers, included, for example, U.S. Pat. No. 3,048,509 and U.S. Pat. No. 4,228,839.
Additionally, other documents include U.S. Pat. No. 7,073,550 B2 to Reiter et al. and U.S. Published Patent Application No. US 2006/0169393 A1 to Botts et al.
U.S. Pat. No. 6,837,287 to Smith Sr. et al. is directed to a method for manufacturing self-sealing pneumatic rubber tires with puncture sealant properties. In the tire building method of Smith, a layer of butyl rubber-based robber composition is assembled into an unvulcanized tire, wherein the butyl rubber composition contains a dispersion therein of precured rubber particles as resin-cured butyl rubber and/or sulfur-cured diene-based rubber, and also containing at least one peroxide that will depolymerize the butyl rubber at the temperatures used to cure the tire. Smith discloses that, in effect, the butyl rubber in the rubber composition is degraded (depolymerized) to a low viscosity to form a tacky material which has puncture staling properties. In the method of this invention, the butyl rubber based rubber composition is assembled into the unvulcanzed rubber tire and the tire is vulcanized using standard known methods which depolymerize and convert the butyl rubber based rubber composition into a sealant layer. In effect it is considered that the peroxide depolymerizes the saturated backbone of the butyl rubber.
Despite the method of Smith it would be useful to have a process for manufacturing self-sealing pneumatic rubber tires, preferably for truck tires, that does not require the use of peroxide.